1. Field of the Invention
The present invention relates to an indirect conversion type radiation detection device for converting incident radiation into light and then converting the light into electric charge.
2. Description Related to the Prior Art
Recently, radiation detection devices for converting incident radiation (e.g. X-rays, gamma rays, or alpha rays) into electric charge and producing radiation image data based on the electric charge have been used. The radiation image data represents distribution of an amount of the incident radiation. There are two types of radiation detection devices: a direct conversion type and an indirect conversion type. The direct conversion type radiation detection device converts the radiation directly into the electric charge. The indirect conversion type radiation detection device converts the radiation into light and then converts the light into the electric charge.
The indirect conversion type radiation detection device includes a light detection section and a scintillator (phosphor layer). The light detection section has a substrate and a plurality of pixels formed on the substrate. The scintillator is layered on the light detection section. Each pixel has a photodiode (PD) and a thin film transistor (TFT). The scintillator is made from CsI, GOS (Gd2O2S:Tb), or the like. The scintillator converts the incident radiation into visible light. The PD of the light detection section converts the light, converted by the scintillator, into the electric charge and stores the electric charge. The electric charge is read out through the TFTs.
The indirect conversion type radiation detection device is classified into a PSS (Penetration Side Sampling) type and an ISS (Irradiation Side Sampling) type. In the PSS type radiation detection device, the scintillator and the light detection section are disposed in this order from a radiation incidence side. Namely, the radiation is incident on the scintillator first. The ISS type, on the contrary, has the light detection section and the scintillator disposed in this order from the radiation incidence side. Namely, the radiation is incident on the light detection section first. The radiation passed through the light detection section is incident on the scintillator. The scintillator converts the incident radiation into the light, and then emits the light in a direction opposite to the radiation incident direction. The PD of the light detection section detects the light. An amount of the light emitted from a radiation incident surface of the scintillator is greater than that from a back face opposite to the radiation incident surface. In the ISS type, the light detection section is disposed close to the radiation incident surface of the scintillator. Accordingly, the ISS type achieves sensitivity and sharpness higher than those of the PSS type.
U.S. Patent Application Publication No. 2008/0290285 (corresponding to Japanese Patent Laid-Open Publication No. 2008-26013) discloses a radiation detection device having a scintillator composed of a plurality of columnar crystals made from CsI or the like. The columnar crystals are arranged such that their end portions face a light detection section. The columnar crystals receive radiation and produce light. Due to the light guide effect of the columnar crystals, the light propagates through the columnar crystals. This reduces scattering of the light emitted from the scintillator and thus improves sharpness of a detection image.
U.S. Patent Application Publication No. 2004/0174951 (corresponding to Japanese Patent No. 3993176) discloses an uneven surface of a light detection section on which light from the scintillator is incident. This increases sensitivity of the indirect conversion type radiation detection device. To be more specific, the uneven surface has a plurality of pyramidal protrusions to improve efficiency of incidence on the light detection section. It has been well known in the field of solid-state image sensors to utilize the uneven surface which varies the refractive index continuously to prevent reflection of the incident light so as to improve the efficiency of incidence (for example, see U.S. Patent Application Publication No. 2010/0244169 corresponding to Japanese Patent Laid-Open Publication No. 2010-272612).
However, when the scintillator has the uneven surface with each columnar crystal tapered or pointed as described in the U.S. Patent Application Publication No. 2008/0290285, or when the light detection section has the uneven surface as described in the U.S. Patent Application Publication No. 2004/0174951, the uneven surfaces may be damaged due to the contact between the scintillator and the light detection section. This reduces sensitivity and sharpness.